The method for obtaining an impact resistant polymer composition by introducing a rubber composition into a hard and brittle thermoplastic resin such as polystyrene, polymethyl methacrylate, styrene-acrylonitrile copolymer, polyvinyl chloride, polyester, polypropylene, polycarbonate, polyimides, or the like, and related blends thereof, has been well known for many years.
The object of this invention is impact resistant polymers and an emulsion polymerization process to produce the impact resistant polymers having industrial advantages.
An impact resistant polymer composition can be obtained by polymerizing a monomer such as styrene, acrylonitrile, methyl methacrylate or the like in the presence of a rubber latex, of which may be produced by emulsion polymerization. It is widely recognized that, in such cases, the particle diameter of the rubber particles greatly governs the impact resistance and processability of the final product, and it is well-known that in some resin matrices, a rubber having a large particle diameter gives improved impact resistance and processability, in comparison to rubbers having small particle diameters.
Accordingly, rubbers such as acrylonitrile/butadiene/styrene (ABS) resins having large particle diameters are a preferred component in impact resistant resins. Dispersed rubber particles found in latices produced by known emulsion polymerization processes generally have small particle sizes (e.g. 40 nanometer (nm.) to 150 nanometer (nm.)), and impact resistance usually cannot be achieved with rubbers having small particle diameters of 40 nm. to 150 nm. Therefore, various processes for producing rubber particles having large particle diameters have been devised and reported.
However, many known processes for producing large particle diameter rubbers have many drawbacks. If an impact resistant resin is produced by such processes, there appear various further disadvantages. Generally speaking, processes for producing large particle diameter rubbers can be classified into two groups. One process for producing rubber particles in the course of polymerization of rubber is known as the "grow-out mechanism", and the other is the process of agglomerating a rubber latex having small size particle by an after treatment, known as "microagglomeration".
The most serious defect of the method in which rubber particles are produced during polymerization is that an extremely long polymerization time is required to complete the polymerization (i.e. greater than 70 hours for particles greater than 300 nm.) For instance, in order to obtain a rubber latex containing rubber particles having a particle diameter of approximately 300 nm., it is necessary to continue the polymerization for 48 to 100 hours. On the other hand, if a rubber latex having a small particle diameter is after-treated to agglomerate the particles, the period of polymerization can be shortened to a great extent. It is extremely difficult to produce a rubber having a large particle diameter by this process. In addition, only a small weight fraction of rubber particles agglomerate. Production of a large particle diameter rubber by this process has always resulted in the formation of high levels of undesirable coagulum. Further, if such a rubber is used for production of an impact resistant graft polymer, the formation of a large amount of coagulum takes place in the course of graft polymerization. Examples of known after-treatment processes to agglomerate particles include: agglomeration by the use of acid, agglomeration by the use of salt, ammonia-soap method, freezing method, solvent treatment method, high pressure treatment method, and polymer colloidal addition method.
The most important disadvantage in the production of large diameter rubber particles and impact resistant polymers by these processes is that special apparatus and reagents needed for the agglomeration of rubber particles must be used. If an impact resistant polymer is produced from monomers and rubbers continuously, for economical advantages, a number of difficulties are encountered. Although no particular apparatus is necessary for agglomerating rubber particles by the addition of an acid or a salt, such an agglomeration process is grounded on a partial destruction of the latex emulsion and the concentration of the aqueous solution of acid or salt, additional velocity of acid or salt, and the speed of stirring, all of which exercise great influence upon the agglomeration behavior of particles. Usually the formation of excessively large particles (coagulum) cannot be prevented, and therefore, it is impossible to produce a rubber having a particle size of 300 nm. or more without formation of coagulum, even though rubbers having a particle size of about 200 nm. can be produced by such processes with relative ease. Further, the addition of the aqueous solution of acid or salt causes lowering of the solid concentration of latex which brings about a decrease in productivity.